OSI Reference Model

The Open Systems Interconnection (OSI) model is a conceptual framework that standardizes network communication functions into seven distinct layers. Each layer provides specific services to the layer above it and receives services from the layer below.

Layer 7: Application Layer

The Application Layer serves as the direct interface between network applications and network services. It handles high-level protocols like HTTP, FTP, SMTP, and DNS, managing user authentication, data privacy, and resource availability.

Layer 6: Presentation Layer

The Presentation Layer manages data format translation, encryption, and compression. It ensures that data from the application layer of one system can be read by the application layer of another, handling character encoding, data compression, and encryption/decryption.

Layer 5: Session Layer

The Session Layer establishes, manages, and terminates connections between applications. It handles session setup, coordination, and termination, implementing checkpointing and recovery mechanisms for long data exchanges.

Layer 4: Transport Layer

The Transport Layer ensures complete data transfer, managing end-to-end communication control. It implements TCP for reliable transmission and UDP for faster, though potentially less reliable, data transfer.

Layer 3: Network Layer

The Network Layer handles logical addressing and routing between different networks. It determines the best path for data transmission, manages IP addressing, and handles packet fragmentation and reassembly.

The Data Link Layer provides reliable point-to-point data delivery over the physical layer. It handles addressing at the hardware level using MAC addresses and manages error detection and correction.

Layer 1: Physical Layer

The Physical Layer defines the electrical, mechanical, and functional specifications for activating and maintaining physical links. It specifies voltage levels, cable types, and signal timing.